1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device realizing a high screen quality by preventing light leakage due to ion adsorption in a signal applying unit.
2. Description of the Prior Art
A liquid crystal display (hereinafter, referred to as LCD) has advantages of light weight, thin thickness and low power consumption, thereby advantageously applied to terminals of information apparatus and video apparatus instead of CRT (Cathode Ray Tube). Especially, TFT-LCD having thin film transistor (hereinafter, referred to as TFT) can realize the high screen quality and can be the large display device, because it has improved response features and is suitable for high number of pixels.
The LCD can be classified into Storage On Gate mode as illustrated in FIG. 1A and Storage On Common mode as illustrated in FIG. 1B by the line design.
As shown in FIG. 1A, the storage on gate mode LCD comprises a gate line 12 and a common line 14 in a signal applying unit 11 out of a display unit 10 realizing image on a substrate 19, applying signals into the display unit 10.
In the storage on gate mode LCD, all the pixels in the display unit 10 have the same structures and they are adjacent to a plurality of pixels comprising a gate line 12, a data line 13, a common line 14, a counter electrode 15, a pixel electrode 16 and a TFT LCD in the same manner.
However, the outmost pixel that is the most adjacent to the signal applying unit 11 has the structure different from other pixels in the display unit 10. Or, a data line is not formed in the direction of the signal applying unit 11 in the outmost pixel.
When a scanning signal is applied to one of gate lines 12 and a display signal is applied to the data line, a TFT 17 disposed at the intersection of the gate line and the data line is turned on. Then, the display signal of data line 13 is transmitted to the pixel electrode 16 through the TFT 17 and the common signal is continuously applied to the counter electrode 15, thereby generating electric field between the electrodes 15,16.
Therefore, liquid crystal molecules (not shown) are arranged to be parallel to the electric field (positive dielectric anisotropy) or to be perpendicular thereto (negative dielectric anisotropy), thereby light leakage is generated and a predetermined image is realized.
Referring to FIG. 1B, the storage on common mode LCD is the same manner.
There are, however, several problems in the conventional LCD.
For gate line and common line, difference between DC (direct current) component signal of gate line and that of common line causes voltage difference. The data line is swung into positive and negative voltage to common voltage in each frame, thereby preventing maintenance of a predetermined DC voltage.
As describe above, the conventional pixel the most adjacent to the signal applying unit has no data line formed in the direction of the signal applying unit. Therefore, ion adsorption is generated due to voltage difference between gate line and common line, and pixels are influenced by the resulting electric field.
In a normally black mode, outmost pixels, which are switched by the electric field generated due to ion adsorption, has a problem of light leakage in a low gray, thereby lowering screen quality.
The present invention has made to solve the above-mentioned problems and the primary objective of the present invention is to provide a LCD preventing light leakage due to ion adsorption in a signal applying unit by extending pixel electrode of outmost pixel to the signal applying unit.
In order to accomplish the objective, the present invention comprises: a substrate; a signal applying unit having a gate line and a common line on the substrate; and a display unit having a plurality of pixels with a data line, a counter electrode, a pixel electrode, a TFT and the gate line and the common line extended from the signal applying unit, wherein the pixel electrode comprises a body unit and a branch unit, the body unit being parallel to the gate line and the branch unit comprising a plurality of branches being parallel to the data line, and pixel electrode of the pixel the most adjacent to the signal applying unit has some of branches formed on the signal applying unit.